Commercially available household-machine dishwasher detergents provided in powder form have several disadvantages, e.g. non-uniform composition; costly operations necessary in their manufacture; tendency to cake in storage at high humidities, resulting in the formation of lumps which are difficult to disperse; dustiness, a source of particular irritation to users who suffer allergies; and tendency to cake in the dishwasher machine dispenser.
Recent research and development activity has focused on the gel or "thixotropic" form of such compositions. Dishwasher products so provided are primarily objectionable in that they are insufficiently viscous to remain "anchored" in the dispenser cup of the dishwasher, and moreover yield spotty residues on dishware, glassware, china and the like. Ideally, thixotropic cleansing compositions should be highly viscous in a quiescent state, Bingham plastic in nature, and have relatively high yield values. When subjected to shear stresses, however, such as being shaken in a container or squeezed through an orifice, they should quickly fluidize and upon cessation of the applied shear stress, quickly revert to the high viscosity/Bingham plastic state. Stability is likewise of primary importance, i.e. there should be no significant evidence of phase separation or leaking after long standing.
U.S. Pat. No. 4,752,409 and U.S. Pat. No. 4,801,395, which are assigned to applicants' assignee and of which the present application is a continuation in part, are directed to thixotropic aqueous suspension dishwashing detergent compositions containing long chain fatty acids and metal salts of long chain fatty acids such as aluminum stearate and sodium stearate as physical stabilizing agents. These compositions show improvement in the physical stability of the detergent composition and improvement against phase separation over those containing compositions that do not contain the aluminum stearate. Although polymeric thickeners are disclosed, they are not exemplified in the specifications even though they are well known in the art.
The provision of automatic-dishwasher compositions in gel form having the afore-described properties, other than for the improvements described in the above mentioned Patent, has thus far proven problematical, particularly in home dishwasher machines. For effective use, it is generally recommended that the automatic dishwashing detergent, hereinafter also designated ADD, contain (1) sodium tripolyphosphate (NaTPP) to soften or tie up hard-water minerals and to emulsify and/or peptide soil; (2) sodium silicate to supply the alkalinity necessary for effective detergency and to provide protection for fine china glaze and pattern; (3) sodium carbonate, generally considered to be optional, to enhance alkalinity; (4) a chlorine-releasing agent to aid in the elimination of soil specks which lead to water spotting; and (5) defoamer/surfactant to reduce foam, thereby enhancing machine efficiency and supplying requisite detergency. See, for example, SDA Detergents in Depth, "Formulations Aspects of Machine Dishwashing," Thomas Oberle (1974). Cleansers approximating to the afore-described compositions are mostly liquids or powders. Combining such ingredients in a gel form effective for home-machine use has proved difficult. Generally, such compositions omit hypochlorite bleach, since it tends to react with other chemically active ingredients, particularly surfactant. Thus, U.S. Pat. No 4,115,308 discloses thixotropic automatic dishwasher pastes containing a suspending agent, e.g. CMC, synthetic clays or the like; inorganic salts including silicates, phosphates and polyphosphates; a small amount of surfactant and a suds depressor. Bleach is not disclosed. U.S. Pat. No. 4,147,650 is somewhat similar, optionally including C1-(hypochlorite) bleach but no organic surfactant or foam depressant. The product is described, moreover, as a detergent slurry with no apparent thixotropic properties.
U.S. Pat. No. 3,985,668 describes abrasive scouring cleansers of gel-like consistency containing (1) suspending agent, preferably the Smectite and attapulgite types of clay at a relatively high concentration of preferably 3-5% by weight; (2) abrasive, e.g. silica sand or perlite, and (3) filler comprising light density powdered polymers, expanded perlite and the like, which has a buoyancy and thus stabilizing effect on the composition in addition to serving as a bulking agent, thereby replacing water otherwise available for undesired supernatant layer formation due to leaking and phase de-stabilization. The foregoing are the essential ingredients. Optional ingredients include hypochlorite bleach, bleach stable surfactant and buffer, e.g. silicates, carbonates, and monophosphate. Builders, such as NaTPP, can be included as further optional ingredients to supply or supplement building function not provided by the buffer, the amount of such builder not exceeding 5% of the total composition, according to the patent. Maintenance of the desired (greater than) pH 10 levels is achieved by the buffer/builder components. High pH is said to minimized decomposition of chlorine bleach and undesired interaction between surfactant and bleach. Foam killer is not disclosed.
In U.K. Patent GB No. 2,116,199B and GB No. 2,140,450B, both of which are assigned to Colgate-Palmolive, liquid ADD compositions are disclosed which have properties desirably characterizing thixotropic, gel-type structure and which include each of the various ingredients necessary for effective detergency with an automatic dishwasher. The normally gel-like aqueous automatic dishwasher detergent composition having thixotropic properties includes the following ingredients, on a weight basis:
(a) 5 to 35% alkali metal tripolyphosphate; PA1 (b) 2.5 to 20% sodium silicate; PA1 (c) 0 to 9% alkali metal carbonate; PA1 (d) 0.1 to 5% chlorine bleach stable, water dispersible organic detergent active material; PA1 (e) 0 to 5% chlorine bleach stable foam depressant; PA1 (f) chlorine bleach compound in an amount to provide about 0.2 to 4% of available chlorine; PA1 (g) thixotropic thickener in an amount sufficient to provide the composition with thixotropy index of about 2.5 to 10; PA1 (h) sodium hydroxide, as necessary, to adjust pH; and PA1 (i) balance water.
Add compositions so formulated are low-foaming; are readily soluble in the washing medium and most effective at pH values best conducive to improved cleaning performance, viz, pH 10.5-14. The compositions are normally of gel consistency, i.e. a highly viscous, opaque jelly-like material having Bingham plastic character and thus relatively high yield values. Accordingly, a definite shear force is necessary to initiate or increase flow, such as would obtain within the agitated dispenser cup of an energized automatic dishwasher. Under such conditions, the composition is quickly fluidized and easily dispersed. When the shear force is discontinued, the fluid composition quickly reverts to a high viscosity Bingham plastic state closely approximating its prior consistency.